The present invention relates to waveguides for microwaves, more specifically to a fluid-tight coupling device for microwave radiation of high energy comprising a waveguide having an input end adapted to be coupled to a microwave source and an output end which is sealed fluid-tight with a dielectric window permeable for the microwave radiation.
For coupling microwaves out of a microwave source and for coupling microwaves from a gas-filled waveguide into a vacuum vessel and similar uses, vacuum-tight or more generally fluid-tight coupling means ("microwave windows") are required. For extremely high microwave powers, for example in the megawatt range, at relatively high frequencies (e.g. above a few 10 GHz, e.g. between 60 and 100 GHz, and relatively large pulse lengths (e.g. several seconds up to continuous waves), as can for example be produced with gyrotrons or free-electron lasers, power densities and thermal stresses occur which are difficult to handle with the known single-pane or multipane windows. For special uses, e.g. the high-frequency heating of a plasma in fusion research, windowless operation of the high-frequency source is therefore being considered. Such an operation however involves considerable disadvantages and great problems.
U.S. Pat. No. 4,297,662 discloses a vacuum-tight high-frequency-permeable window arrangement between an input and an output coaxial line in which between the input and the output coaxial line a ceramic hollow cylinder is disposed which surrounds the inner conductor of the input coaxial line in the region of the transition to the output coaxial line as continuation of the outer conductor of the input coaxial line. For adaptation of the input coaxial line to the output coaxial line in the region of the window arrangement adapting elements are provided, for example an annular adapting element which surrounds the ceramic hollow cylinder in spaced relationship and is mounted at the inner side of the inner conductor of the output coaxial line. These adapting elements are not suitable for waveguides not having any inner conductor.